Restructuring

    for a in distinct(bib0/book/author) do
      biblio [
        a,
        for b in bib0/book do
          for a2 in b/author do
            where a/data() = a2/data() then
              b/title
      ] 
==> ...
    biblio [
      author [ "Suciu" ],
      title  [ "Data on the Web" ],
      title  [ "XML Query" ]
    ], ... 
:   biblio [
      author [ String ],
      title  [ String ] {0,*}
    ] {0,*}